Fixing device and method for fixing to a substrate

ABSTRACT

A fixing device including a shank and a head. The shank has formed thereon a helical thread configuration including a pair of spaced helical ridges with a helical groove defined therebetween. The height of the ridges is reduced at both ends of the shank with their height gradually increasing over one convolution from an end opposite the head, and decreasing over half a convolution to an end nearest the head.

The invention relates to an improved fixing device having particular,but not exclusive, application in fixing to a substrate, such as timber,plastics materials and friable substrates, such as timber end grain,plywood, blockboard and sterling board edge face, MDF and other particleboard (eg chipboard or fibre board), light-weight autoclaved aeratedconcrete in, for example, block form (eg of the type sold under thetrade marks “Thermalite”, “Celcon” and “Durox”), plaster, render, softred brick, breeze (eg breeze blocks) and other friable masonrysubstrates.

Conventional threaded fixing devices such as screws are difficult tosecure in masonry substrates since it is difficult for a conventionalthread to find secure location within a bore in such a substrate.Conventional screw threaded fixings are accordingly conventionallysecured within bores in masonry substrates by first lining the bore witha lining of relatively soft material into which the threaded fixing cancut its own thread, at the same time compressing the lining against thewalls of the bore within the masonry substrate. A typical example ofsuch a lining is that sold under the trade mark Rawlplug. Such liningsare available in fibrous and plastics material form and in a widevariety of configurations reflecting a very considerable activity in theart over the years to improve upon the security and ease of use of screwthreaded fixing devices used with such liners.

Adopting a somewhat similar principle, alternative forms of fixingdevice are of metallic material and structured so as to be expansibleafter introduction into a bore in a masonry material whereby compressiveforces against or impingement into the internal surfaces of the boreresist withdrawal of the fixing device from the bore. Reflectingsimilarly substantial activity in the art, a wide variety of suchdevices are available. For example, various devices of this kind areavailable under the above-mentioned trade mark Rawlplug and under thetrade marks Fischer and Hilti.

Fixing devices somewhat similar to those sold under the trade markRawlplug are also sold under the trade mark Fischer, as mentionedearlier. The Fischer Wallbolt comprises a segmented malleable ironexpander shield forming a sleeve about an orthodox screw threaded bolt.The combined assembly is in use inserted into a pre-drilled bore in amasonry substrate and the bolt is tightened with a spanner. This draws aterminal conical wedge backwards into the shield and forces four shieldsegments outwardly against the sides of the bore.

All fixing elements which rely on compression of an associated memberinto the wall of a pre-drilled bore give rise to structuraldisadvantages. The walls of the bore are placed under stress and in manysubstrate materials there is insufficient strength in the substratestructure to prevent cracking. This is particlarly the case with suchmaterials as lightweight autoclaved aerated concrete but also applies tobrick structures. It is especially evident adjacent apertures in amasonry structure where on one side at least there will be comparativelysmall thickness of substrate material. Of course, fixing elements arecommonly required in aperture regions for the fixing of window frames,door liners and similar fittings.

Equally, a good deal of activity has been focused on improvement ofscrew threaded members themselves in order that they should find securefixing in masonry materials without the use of liners and withoutinternal expansion. The driving force in these respects is, of course,the fact that liners do not provide totally satisfactory degrees ofsecurity, the fact that the need to insert a liner in a bore representsan additional activity which has associated labour costs and the factthat in the case of expansion bolts and such like the compressive forcesnecessary for security of fixing can result, as noted above, in ruptureof masonry materials particularly when adjacent to extremities of bodiesof such materials.

UK Patent Specifications Nos 2 115 511 (ITW III) and 2 152 171 (ITW II)disclose masonry fixings comprising a shank having spaced threads in theform of a helical ridge alternating with a parallel land. The flanks ofthe threads intersect at an angle of 50° to 65° and exhibit a helixangle of 6° to 8.5°. These features are necessarily combined withspecial conditions for introduction into a masonry bore and are claimedto provide security of fixing without thread striping upon insertion.Both ITW II and III represent examples of effort in the art to providethreaded devices for direct securement in a bore so as to avoid thedisadvantages of expansion-type devices enumerated above.

Coarse deep threads are also disclosed in a fixing for use inmasonry-like structures in UK Patent Specification No 1 510 686 (ITWIV), a further example of an attempt to provide a direct-fixture fixingelement. In this particular arrangement, the crests of the deep threadsare notched in order to assist in the cutting of a thread by the fixturein use and to assist in the transmission of masonry debris within thebore. An intermediate shallower thread ridge appears to be the key toproviding a design which enables security of fixture to be achievedwhilst at the same time recognizing the need to minimize disturbance ofthe substrate material. Nevertheless, threads penetrate the substrate atfairly closely spaced positions such that pull-out performance isimpaired by the shear resistance of the relatively small sections ofsubstrate material between helical ridge turns. A similar arrangement isdisclosed in European Patent Application No 0 133 773 (ITW I).

UK Patent Specification No 466039 (Jasper) discloses a fastening screwhaving a shank provided with a helical thread groove alternating with aland between the grooves. A longitudinal slot provides self-tappingcapacity for the coarse deep thread. Jasper does not disclose thefastening screw for use in masonry structures.

A somewhat similar screw device is described in UK Patent SpecificationNo 274833 (Rosenberg). The entry end screw thread configuration has agroove which penetrates the normal diameter of the fixing devicetogether with raised border ridges, this configuration extending over ashort length only of the shank. Rosenberg does not recommend the fixingdevice for masonry fixing, referring generally to fibrous andnon-flowing materials and in particular to metal substrates.

European Patent Specification No 0 225 003 (JSM) and UK PatentApplication No 2036227 (Tomoyasu) disclose self-locking screws having asomewhat similar configuration. Helical ridges either side of a smallland have their crests grooved. Tomoyasu also refers to a structure inwhich the ridge crests are not grooved but an intermediate ridge isturned through the land so that there are in fact two parallel groovesforming an overall thread. Both JSM and Tomoyasu relate to self-lockingdevices reliant on the interaction of male and female threads and thereis no disclosure of a use in which the male threaded portion isself-tappingly threadedly into a masonry bore.

UK Patent Specification No 2042120 (Gutshall) discloses a headed screwwhich incorporates a long-pitch helical thread rolled on a cylindricalblank. The rolling leaves untouched a land between adjacent convolutionsof the thread. At each juncture between the root of the thread and theadjacent land a helical crest functioning as an auxiliary thread isprovided to improve the holding power of the screw. Gutshall refers touse of the disclosed screw in soft, fibrous or low-density materialswhich are exemplified as wood and plastics. Gutshall does not appear torecommend the disclosed headed screw for fixture self-tappingly in amasonry substrate.

UK Patent Specification No 1541237 (Oratronics) discloses a threadeddevice for use as an endodontic stabilizer. The shank of the discloseddevice is turned with a helical groove having a sufficiently wide pitchto provide a parallel inter-turn land. The crest of the ridge isgrooved. UK Patent Specification No 1519139 (Crock) discloses a simplerstructure for use in surgical techniques. The structure disclosedcomprises a threaded shank comprising a thread groove somewhatreminiscent of that shown by Rosenberg as mentioned above. Crock refersskirtingly and somewhat speculatively to application in buildingconstruction and associated fields but there is no referencespecifically to the use of the disclosed device for self-tappinglysecuring in a masonry bore.

In PCT Application No WO 92/10688, fixing to masonry substrates (egbrickwork, blockwork or concrete) involves forming a bore in thesubstrate (eg in the tension zone or compression zone of a concreteload-supporting member such as a concrete beam) for a fixing device,introduced into the bore self-tappingly or otherwise, which comprises ashank having a bore entry end and an opposed optionally headed endseparated from the bore entry end by the length of the shank, at least aportion of the shank length being configured with a thread rolledhelical groove depressed into the blank circumference of the shank so asplastically to displace shank material to at least one of the groovesides, the groove being defined adjacent a helical ridge juxtaposed to aside of the groove or between a pair of parallel helical ridgesjuxtaposed one either side of the groove and formed in either case ofthe plastically displaced shank material. The ridges are upstanding fromthe blank circumference of the shank so as to function in use each as amale thread, at least the leading end of the thread preferably being afemale thread-cutting male thread in relation to the masonry. Thehelical ridges and defined helical groove form a helical configurationwhose convolutions are spaced apart by an intervening land in relationto which the ridges are raised and the groove is depressed. The land hasa width measured axially with respect to the shank of at least 50% ofthe land shank diameter and the helix angle of the helical ridge is atleast 8° and preferably 10° or more. The fixing device is ordinarilyinserted into a slightly oversized bore (and thus the shank of thedevice will be slightly undersized in terms of diameter relative to thedrill diameter used to produce the bore).

Many modern and some traditional construction materials are friable innature and do not support high pull-out strengths for fixing devicesfixed in them. The reasons for this are manifold. For example, in manyfriable materials a fixing will not self-thread into a predrilled borebecause the initial turns of the fixing do not start a helical channelin the bore, but simply enlarge the outer extremity of the bore byabrasion of substrate material. Many devices which can be threaded intoa bore self-tap, but have a propensity for overtorque damage, the boreincreasing in cross-section over its length to that of the circumferenceof the threaded surface of the fixing. These problems are particularlyprevalent in autoclaved aerated concrete such as in building block form,but are also found when fixing to such traditional materials as soft redbrick (and bricks made of differently coloured fired clays) and plastersand renders made of eg lime plaster/render mixes. Timber substrates posedifferent problems, but in many cases pull-out strength requirementsmean that a fixing must pass through a timber member and be secured by anut on a face opposed to the face through which the fixing isintroduced, the latter normally being engaged by a head of the fixing.This means certain constraints when fixing together two members whereone face is inaccessible for securement of a nut. Timber end grain isnotoriously poor as a fixing base for a fixing device. This is indeed somuch so that it is rare to rely solely on screw thread engagement intimber end grain in any real life situation; of course, nut securementis usually precluded in the case of fixings in timber end grain.

According to the invention, there is provided, in a first aspect, afixing device for fixing into a substrate, the fixing device comprisinga shank having a first end and a second end and an optional head at thesecond end, wherein the shank of the fixing device is configured with atleast one helically extending thread upstanding to a full height fromthe shank in a plurality of convolutions around the shank, wherein thethread has a height above the shank which is reduced adjacent the firstend of the shank and which gradually increases to its full height.

In a preferred embodiment, the height of the thread increases from thereduced height to the full height over at least a first convolution ofthe thread adjacent the first end.

Preferably, the reduced height is no more than 50% of the full height.

Preferably, the reduced height is at the level of the shank.

In one preferred embodiment, the thread gradually decreases in heightfrom its full height as it approaches the second end of the shank.

Preferably, the height of the thread decreases from the full height to alesser height over at most a final convolution of the thread adjacentthe second end.

Preferably, the lesser height is at the level of the shank.

Preferably, the height of the thread decreases from the full height tothe lesser height over half of the final convolution of the threadadjacent the second end.

In a preferred embodiment, the shank of the fixing device is configuredwith a plurality of helically extending threads upstanding from theshank and wherein each of the threads has a height above the shank whichis reduced adjacent the first end of the shank and which graduallyincreases to its full height.

Preferably, the shank of the fixing device is configured with a pair ofparallel threads upstanding from a helically extending land to definetherebetween a helically extending groove. The groove may extend belowthe level of the land. The pair of threads preferably have the sameheight above the land.

In a second aspect, the invention provides a fixing method whichcomprises turning into a bore in a substrate a fixing device as definedabove according to the invention, the bore having a diameter less thanthe diameter of the fixing device shank, the fixing device beingutilised to fix a member to the substrate.

Preferably, the substrate is composed of timber or friable masonrymaterial, such as autoclaved aerated concrete, a cured plaster or rendercoat, plasterboard or soft red or other soft brick.

In particular, the friable masonry material may be masonry materialhaving a crush resistance of less than 5N/mm², for example a crushresistance of less than or equal to 3.5N/mm².

The friable masonry material may be cementitious or clinker-based.

In the case of timber substrates, the timber substrate is in particulartimber end grain. In such cases, the fixing device is turned into thebore in the substrate by application of axial force. The application ofaxial force may be application of intermittent dynamic force along theaxis of the shank of the fixing device. In particular, the axial forcemay be a percussive force applied by hammering.

An embodiment of the invention will now be described, by way of exampleonly, with reference to the accompanying drawings of which:

FIG. 1 shows an embodiment of a fixing device according to theinvention; and

FIG. 2 is a schematic cross-sectional view of the fixing device of FIG.1 showing the threads in an exaggerated, enlarged scale.

The fixing device 10 shown in FIG. 1 of the drawings comprises a brightzinc plated steel shank 1 of solid right circular cylindrical form. Theshank is formed by cold forming with a head 2 at one end 13, which is inconventional hexagonal form comprising six faces 5 intended for locationin the jaw of an open spanner of complementary size and shape or by asuitable socket or ring spanner. Obviously, however, the head 2 may beformed with a different type of head such as a countersink headconventionally slotted as for conventional blade screwdriver engagementor formed with a Posidrive screw engagement depression. Alternatively,the head may be formed for a so-called TORX or HEX drive, or any otherkind of drive, as will be appreciated by those skilled in the art.

The end 3 of shank 1 opposed to head 2 is formed with an annular cant orbevel 4 intended to assist in introduction of the tip of the shank intoan appropriately sized and configured bore in a substrate.

Shank 1 is formed by thread rolling with a helical bore wall engagementconfiguration designated generally by reference numeral 6. Thisconfiguration comprises a pair of spaced apart helical ridges 7 and 8.Both helical ridges 7 and 8 are formed on shank 1 with identical helixangles with the result that the ridges are, of course, parallel one toanother and separated by the same pitch throughout the extent of thehelix. Both ridges serve as a screw thread for fixing the fixing devicein a bore in an appropriate substrate. Both ridges are of generallyfrusto-conical form in cross-section. Each ridge has an upstand from thesurrounding basal surface of the shank 1 which is uniform throughout thehelix, with both upstands being the same as one another. Ridge 7 defineswith ridge 8 a helical groove 9 forming part of helical engagementconfiguration 6.

The turns of helical bore wall engagement configuration 6 are separatedby turns of a helical land 11. The groove 9 may have a depth thatextends to the same level as the land 11, such that the groove is simplydefined between the threads 7 and 8, or the depth of groove 9 may extendbelow the level of the land 11 such that it is cut out of the shank 1.For example, the groove may extend approximately 0.5 mm below thesurface of the shank. The groove itself may have any desired width, forexample a width of between 2 mm and 10 mm.

It will be apparent that the screw thread arrangement has a pitch, whichis indicated by reference numeral 12 in FIG. 2, which is equivalent, inan axial direction of the device to one convolution of the threadconfiguration 6 about the shank 1. The ridges 7 and 8 have a heightabove the level of the land 11 which is substantially constantthroughout the length of the shank 1, except at the two ends 3 and 13thereof. At the end 3 opposite the head 2, the height of the ridges 7and 8 is decreased in a constant fashion, so that they have a reducedheight nearest the end 3. The reduced height is 50% of the full heightand the ridges gradually taper up to the full height over at least halfof the first convolution 14 of the thread configuration 6, andpreferably over the whole length of the first convolution 14. In otherembodiments, the reduced height may be 25% of the full height, or mayeven be zero, i.e. at the level of the land 11. Furthermore, the depthof the groove 9 below the level of the land 11 may also reduced, so thatthe depth gradually increases over the first convolution of the threadconfiguration to its full depth.

Reduction of the height of the threads 7 and 8 at the end 3 reduces theamount of torque required to turn the device into a substrate. Althoughsuch holes are usually pre-drilled, the hole diameter is at most that ofthe shank, so that the threads must cut into the substrate. By reducingthe torque needed to turn the device, it becomes much easier to insertthe device into the substrate thereby reducing the amount of strainexerted on the material of the device (usually steel), so that itsintegrity is maximised. Binding of the device to the substrate materialduring installation is also minimised.

By having the thread tapered, the first convolution of the threadtherefore only cuts the substrate to a reduced depth, as compared toknown threads which perform a full depth cut by the first convolution,so that the following convolution of the thread also has some cutting toperform. Therefore, the threads are less likely to lose their cuttingedge, especially cutting into dense concrete and are less likely toflatten, as happens in known devices. The height of the threads cantherefore be increased in height, for example by at least 25% over knowndevices, thereby gaining deeper penetration into the substrate andtherefore increasing the tensile loading, if required.

Similarly, the height of the ridges 7 and 8 is decreased in a constantfashion at the end 13 nearest the head 2, so that they have a reducedheight nearest the head 2. The reduced height may again be 50% of thefull height and the ridges gradually taper down over half of oneconvolution 15 of the thread configuration 6. As before, the reducedheight may be 25% of the full height, or may even be zero, i.e. at thelevel of the land 11. Furthermore, the depth of the groove 9 below thelevel of the land 11 may also gradually reduced over the last halfconvolution so that it does not extend below the level of the land 11near the head 2.

Reduction of the height of the threads 7 and 8 at the end 13 reduces theamount of strain exerted on the material of the device, so that thestrength of the device, particularly at the point where the shank meetsthe head 2 is improved. Reduction of the depth of the groove alsoreduces any such weaknesses. The torque applied to the device byoperatives during installation can therefore be increased withoutcompromising the integrity of the fixing.

It will be appreciated that the fixing device may be made in a range ofsizes. The particular parameters of a fixing device other than diameter(ie M size) will vary according to the M size of the fixing device.Fixing elements according to the invention can be manufactured by thesteps of cold-forging and thread-rolling, bright zinc plating and heattreatment without resort to complex assembly operations such as arenormally associated with an expansion bolt. This produces economies interms of materials and manufacturing costs as well as the economiesassociated with relative ease of installation and use noted below.

It will be appreciated from the foregoing that the invention is simpleto use in practice, the device readily self-tapping when turned into abore in a variety of materials. The device holds firmly in timber endgrain and on continued turning its head, if any, will perforate andembed in the timber. Even a high degree of rotation will not cause thedevice to ream the bore of an autoclaved aerated concrete block, butrather self-threading penetration continues. Over-torquing is per segenerally impossible in soft red bricks. Under ultimate tensile loads inmost substrates the device does not fail or cone out the substrate. Asthe tensile load is increased the bolt starts to withdraw but as eachconvolution of the thread emerges the following convolution takes thetensile load back to its ultimate. This gives the device a fail-safecharacteristic. When hammered into a predrilled hole into end and crossgrained timber the bolt turns on impact and cuts its own threadperfectly into the timber. The clamping force timber to timber isexcellent in both end and cross grain situations. It will replace thenecessity to use standard nuts and bolts. The product can be removed byunscrewing even though it has been hammered in.

Whilst only one particular embodiment of the invention has beendescribed above, it will be appreciated that a person skilled in the artcan make modifications and improvements without departing from the scopeof the present invention. For example, although the invention has beendescribed with a particular thread configuration of a pair of parallelthreads defining a groove therebetween with a land extending between theconvolutions of the thread configuration, other thread configurationsare possible within the scope of the invention, provided the thread hasa height above the shank which is reduced adjacent the first end of theshank and which gradually increases to its full height. In particular,the invention can be applied to single threaded, double threaded ormultiple threaded fasteners, whether or not they have defined groovesbetween the threads.

1-25. (canceled)
 26. A fixing device for fixing into a substrate, thefixing device comprising a shank having a first end and a second end andan optional head at the second end, wherein the shank of the fixingdevice is configured with at least one helically extending threadupstanding to a full height from the shank in a plurality ofconvolutions around the shank, wherein the thread has a height above theshank which is reduced adjacent the first end of the shank and whichgradually increases to its full height.
 27. A fixing device according toclaim 26, wherein the height of the thread increases from the reducedheight to the full height over at least a first half-convolution of thethread adjacent the first end.
 28. A fixing device according to claim26, wherein the height of the thread increases from the reduced heightto the full height over at least a first full convolution of the threadadjacent the first end.
 29. A fixing device according to claim 26,wherein the reduced height is no more than 50% of the full height.
 30. Afixing device according to claim 29, wherein the reduced height is nomore than 25% of the full height.
 31. A fixing device according to claim30, wherein the reduced height is at the level of the shank.
 32. Afixing device according to claim 26, wherein the thread graduallydecreases in height from its full height as it approaches the second endof the shank.
 33. A fixing device according to claim 32, wherein theheight of the thread decreases from the full height to a lesser heightover at most a final convolution of the thread adjacent the second end.34. A fixing device according to claim 33, wherein the height of thethread decreases from the full height to the lesser height over half ofthe final convolution of the thread adjacent the second end.
 35. Afixing device according to claim 33, wherein the lesser height is at thelevel of the shank.
 36. A fixing device according to claim 26, whereinthe shank of the fixing device is configured with a plurality ofhelically extending threads upstanding from the shank and wherein eachof the threads has a height above the shank which is reduced adjacentthe first end of the shank and which gradually increases to its fullheight.
 37. A fixing device according to claim 26, wherein the shank ofthe fixing device is configured with a pair of parallel threadsupstanding from a helically extending land to define therebetween ahelically extending groove.
 38. A fixing device according to claim 37,wherein the groove extends below the level of the land.
 39. A fixingdevice according to claim 38, wherein the groove has a depth below thelevel of the land which is reduced adjacent the first end of the shank.40. A fixing device according to claim 38, wherein the groove has adepth below the level of the land which is reduced as it approaches thesecond end of the shank.
 41. A fixing device according to claim 37,wherein the pair of threads have the same height above the land.
 42. Afixing method comprising turning into a bore in a substrate a fixingdevice comprising a shank having a first end and a second end and anoptional head at the second end, wherein the shank of the fixing deviceis configured with at least one helically extending thread upstanding toa full height from the shank in a plurality of convolutions around theshank, wherein the thread has a height above the shank which is reducedadjacent the first end of the shank and which gradually increases to itsfull height, the bore having a diameter less than an external diameterof the fixing device including the at least one thread, the fixingdevice being utilized to fix a member to the substrate.
 43. A fixingmethod according to claim 42, wherein the substrate is composed oftimber or friable masonry material, such as autoclaved aerated concrete,a cured plaster or render coat, plasterboard or soft red or other softbrick.
 44. A fixing method according to claim 42, wherein the fixingdevice is turned into the bore in the substrate by application of axialforce.
 45. A fixing method according to claim 44, wherein theapplication of axial force comprises application of intermittent dynamicforce along the axis of the shank of the fixing device.
 46. A fixingmethod according to claim 44, wherein the axial force comprises apercussive force applied by hammering.